In the production of seamless tubing, it is conventional for a heated, cylindrical workpiece to be simultaneously rotated and driven over a piercing mandrel to form a tube. The pierced, tubular workpiece may then be directed to a plug mill, for enlarging of diameter and reduction of wall thickness, and then further directed to a reeling operation where the workpiece is rapidly rotated and passed over a mandrel to improve roundness. In all of the before described operations, of piercing, sizing in the plug mill, and reeling, the workpiece is driven over a mandrel which carries at its upstream end a mandrel plug of appropriate size and shape. In each instance, after passage of a workpiece over the mandrel, the mandrel plug is removed from the mill for cooling and is replaced by a fresh plug. Efficient and advantageous arrangements for expediting the change of mandrel plugs in a plug mill are described and claimed in the related, copending application of Russell Jones, entitled "Plug Changer for Plug Mill" Ser. No. 682,920, filed May 4, 1976. The present invention is directed more particularly to techniques for the changing of the mandrel plugs in piercing and reeling mills.
In accordance with one aspect of the invention, a magazine, for retaining a circulating inventory of mandrel plugs, is movably mounted on the downstream side of the mill rolls. The magazine has a plurality of pockets for retaining mandrel plugs, and has a working position located generally directly below the pass line of the mill and at an upwardly inclined angle intersecting the pass line slightly downstream of the working bite of the mill rolls. Fresh mandrel plugs are successively brought into the working position, from which they are advanced along an upwardly inclined transfer chute, by means of a plug pusher ram. A portion of the transfer chute may be mounted for pivoted movement such that, when a fresh mandrel plug is positioned on the pivoting section, it may be swung upward into the pass line of the mill to facilitate joining of the mandrel plug and the mandrel. In other cases, the upper section of the transfer chute may be so contoured as to enable the mandrel plug, as it is elevated along the transfer chute by the pusher mechanism, to be properly aligned with the pass line axis of the mill.
In piercing and reeling mills, the working rolls of the mill are mounted in a horizontally opposed arrangement, and the workpiece is supported between the rolls by means of longitudinally grooved mill shoes, which confine the workpiece vertically while permitting it to rotate and advance longitudinally. These mill shoes are subject to substantial wear and must be replaced with relative frequency. Accordingly, it is an additional aspect of the invention to provide a novel arrangement for mounting and securing mill shoes in a piercing or reeling mill, such that the down time involved in effecting a change of mill shoes may be significantly reduced as compared to conventional means. More particularly, the upper mill shoe is secured by a releasable clamp, which enables the shoe to drop down onto the lower shoe (or onto to a filler block inserted between the shoes). The lower mill shoe is mounted on a horizontal slide mechanism, and this mechanism is actuated after the upper shoe has been released and serves to simultaneously unclamp the lower shoe and to physically deliver the unclamped upper and lower shoes to an accessible position on the downstream side of the mill rolls. The mill shoes are thus easily accessible to an overhead hoist or crane, for easy removal and replacement. After new shoes have been put into position, the horizontal slide mechanism is retracted back into the area of the mill bite, which not only carries the mill shoes back into the working area but locks the lower shoe and its adapter into position, automatically, when the mechanism reaches its working position. The upper mill shoe is then engaged and locked into position by its clamping mechanism, after which the mill is again ready for operation.
As a further feature of the invention, provision is made for simplifying and expediting the complete removal from the mill of the so-called chair assembly which adjustably supports the upper mill shoe and its adapter, in order to facilitate change of mill shoes and mill shoe adapters for accommodation of a new size of tubing in the mill. To this end, the chair assembly for the upper mill shoe is adjusted and locked into position by a combination of upwardly acting fluid cylinders and downwardly acting screw-downs. To effect complete release of the chair assembly, the hydraulic cylinders are retracted slightly, and the downwardly acting screw-downs, advantageously in the form of Tee-headed bolts, are manipulated to a release orientation, enabling the upper chair and its support to be bodily removed from the mill. After change of the mill shoe adapter and/or of the upper chair itself, if necessary, the entire assembly is reinserted into the mill cap, the Tee-headed screw-down bolts are turned to a locking orientation, and the assembly is locked back into position by energizing of the upwardly acting cylinders. An important practical advantage of this arrangement is that the upwardly acting fluid cylinders, in continuously urging the mill cap upward against the T-headed screw downs, eliminate backlash in the hold-down system.
All the various features of the invention are designed to expedite the non-productive aspects of mill operation, particularly change of mandrel plugs and change of mill shoes and adapters, such that the mill can be maintained in production operation during a maximum percentage of its working time. Because of the extremely high capital costs of such mills, it will be readily understood that important advantages can be achieved by increasing the actual production output of a given mill through reduction of down time.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of certain preferred embodiments of the invention, and to the accompanying drawings.